Known flat-screen image display devices (hereinafter also referred to as “displays”) are based on a liquid crystal system, an organic EL (electroluminescence) system, or an inorganic EL system.
The liquid crystal system is limited in contrast, as it forms an image from white light from a backlight with a liquid-crystal shutter and a color filter. Further, the liquid crystal system tends to be high in power consumption, as it is low in efficiency in the use of light. Furthermore, the liquid crystal system is narrow in its color gamut, as the red (R), green (G), and blue (B) color filter has such a wide transmission band that there is an overlap with an adjacent band.
On the other hand, the organic EL system is superior to the liquid crystal system in terms of contrast, power consumption, and color purity. However, since the organic EL system is more difficult to manufacture than the liquid crystal system, the organic EL system has yet to be sold on a full scale. It should be noted that although the sale of an organic EL display including a combination of a white EL and a color filter has recently been launched, such an organic EL display shows no profound improvements in its color gamut and power consumption, albeit with improved contrast.
The inorganic EL system is a system in which an image is formed by light-emitting elements formed by compound semiconductors, configured to emit RGB colors of light, and spread all over a screen. Inorganic EL displays are being put into practical use as supersized displays on racetracks, in stadiums, and elsewhere. For example, in the International Consumer Electronics Show held in the United States in 2012, a test model of the 55-inch full high-definition standard called “Crystal LED Display” was displayed (see, for example, NPL 1).
Since liquid crystal displays and organic EL displays each include a glass substrate, a thin-film transistor formed on the glass substrate, and a liquid crystal or organic EL layer formed on the thin-film transistor, larger displays lead to more complicated steps, undesirably resulting in lower yield rates and higher prices. Further, a thick glass substrate is needed to ensure heat resistance and strength that are necessary to the conduct of a thin-film process, undesirably resulting in a heavier display. To address these problems, an attempt to form a display on a flexible resin substrate has been made but is currently a far cry from commercialization. Further, an attempt to form a thin-film transistor on a resin substrate has also been launched but has not reached a practicable level.
Meanwhile, since inorganic EL displays are superior in performance than light crystal displays and organic EL displays, there have so far been proposed various method for producing an inorganic EL display. However, since a practical structure suited to mass production has yet to be achieved, a shift to mass production has yet to made.
As a method for producing an inorganic EL display, Japanese Patent No. 4082242 (PTL 1) discloses, for example, a method including placing LED (light-emitting device) chips on a temporary holding substrate, embedding the LED chips into an adhesive layer of a transfer substrate, hardening the adhesive layer, forming a wiring layer, pasting a supporting substrate to the adhesive layer again, peeling the transfer substrate, boring a contact hole through the adhesive layer, forming another wire, and thereby forming an LED chip array on the supporting substrate.
Further, Japanese Patent No. 4491948 (PTL 2) discloses a method including performing a thinning-out transfer with a laser irradiation peeling technique from a microchip array in which LED chips are arrayed, thereby forming, on another substrate, LED chips arrayed at enlarged pitches of substantially an integral multiple of chip size, and retransferring these LED chips onto a supporting substrate.
Japanese Patent No. 4479827 (PTL 3) includes peeling, from a substrate for use in compound semiconductor growth, LED chips formed with p-side electrodes, transferring the LED chips into a temporary fixing substrate, further forming n-side electrodes on the temporary fixing substrate, and performing a thinning-out transfer onto a relay substrate with a laser peeling technique. The R, G, and B LED chips thus arrayed are transferred onto a first transfer substrate to form a pixel array, and on this substrate, transparent electrodes and n-side metal wires are formed. Furthermore, after a transfer from the first transfer substrate to a light-emitting unit substrate, through which p-side contact holes are bored and on which p-side wires are formed, the light-emitting unit substrate is pasted to a substrate for display device via a second transfer substrate. With a driving wiring layer formed over the substrate for display device, a display device is completed through a contact hole forming step and a wiring step for connecting, to driving wires, the p-side wires and n-side wires connected to the LED chips.